﻿using System;

class Circle
{
    private double radius; // 半径
    private const double PI = Math.PI; // 圆周率

    // 构造方法
    public Circle(double radius)
    {
        this.radius = radius;
    }

    // 获取周长：2πr
    public double GetPerimeter() => 2 * PI * radius;

    // 获取面积：πr²
    public double GetArea() => PI * radius * radius;
}

// 测试类
class Program
{
    static void Main(string[] args)
    {
        Circle circle = new Circle(5);
        Console.WriteLine($"圆的周长：{circle.GetPerimeter():F2}");
        Console.WriteLine($"圆的面积：{circle.GetArea():F2}");
    }
}